Optimization of ethanol-modified subcritical water extraction of curcuminoids from turmeric (Curcuma longa L.) rhizomes: Comparison with conventional techniques

Subcritical solvent extraction (SSE) as ethanol-modified subcritical water extraction (SWE) was applied to extract curcuminoids from turmeric (Curcuma longa L.) rhizomes. RSM-CCD was employed to evaluate the influential factors including temperature (90-150 degrees C), flow rate (1-4 mL/min), and ethanol concentration (25-75 wt%) on the extraction yield. The optimum condition was 90 degrees C, 4 mL/min, and 25 wt% with the extraction yield of 4.12 wt% (db). Applying ethanol as a polarity-tuning parameter enabled operations at lower temperatures, which prevented thermal degradation. The SSE optimum experiment was compared with Soxhlet, ultrasound-assisted extraction (UAE) and con-ventional solvent extraction (CSE), both with the ethanol-water mixture (25 wt%). Their yields were 2.71, 0.85, and 0.84 wt% (db), respectively. The higher yield of SSE was related to the higher solubility of curcuminoids due to the more appropriate adjustment of solvent polarity by a decrease in the dielectric constant with a rise in the operating temperature.

Automated summary

Subcritical solvent extraction (SSE) combined with ethanol-modified subcritical water extraction (SWE) was used to extract curcuminoids from turmeric. The influential factors, including temperature, flow rate, and ethanol concentration, were evaluated using response surface methodology. The optimal conditions were determined as 90 degrees C, 4 mL/min, and 25 wt% ethanol concentration, resulting in a yield of 4.12 wt%. Ethanol as a polarity-tuning parameter allowed for operations at lower temperatures, preventing thermal degradation.